Very simply,
go to WhitePages.com, Switchboard.com, YellowPages.com
and WhoCalled.us and run reverse lookups.

In almost
every case, if the number is at least a few months old, it will
be listed online at one of those locations - and if it's not
in the United States, then see if there are variants of the
site for your region - such as WhitePages.ca for Canadians,
etc.

Reverse
lookups can become difficult if the number is one of the following:

a)
Too "new" to be listed in a database - or switched
to a new user that's not the correct one listed

b)
Unlisted or commercial (if not listed in the YellowPages or
business directories)

c)
Cellular, pager or otherwise wireless phone number

To discover
how to find information on those types of numbers, you'll need
to read these articles:

However
- some of the strategies listed in those articles are "controversial"
at best, and might not even be legally viable in some
areas!

For this
reason, you should also know that you can also use the national
records database search at Reverse
Phone Detective, which is inexpensive and legal.
They have about an 80% success rate based upon my own experience
with them. It will cost you a small fee, but it's also a
legal source and you won't have to play "private detective"
or risk breaking any laws to find out what you need to know.

You
can actually search their database directly from this form below...

Step
1:Enter
a Cell Phone Number to Search

Enter the
cellular, residential or other type of phone number you'd like
to lookup, then click the button below...

(Number
Format should be 555-555-5555 or 1114442222)

Tutorial:

Enter
the phone number of the person you wish to investigate in the
search box above, and press "search".

Within
seconds, you will be notified as to whether or not the full
record exists in the premium database. If it does, click "Continue",
and then for a small fee, you can access the person's complete
details, which may include:


Full Name


Address


Date of Birth


Carrier/Wireless Company


And the additional (bonus) background-search features included
in the member portal may provide details including background
information, criminal history, driving records, asset details,
property records and more...